Not much really. I think its really stupid of the Spanish Govt. to try to stick to formal constitutional means when there is a genuine, popular mandate for independence. What they seem to be saying is that a referendum is not allowed by current laws so it is illegal to have it. And their ham handed response is only agitating the region even more, legitimizing the separatists call for independence.
OTOH if they had provided a path for an actual referendum to be held, provided democratic means for allowing independence... who knows? Maybe there wouldn't be a popular mandate in the referendum. Maybe the central government could have worked closely with those people, parties and cities that wanted to continue being part of Spain and convinced more.
Its seems really rich of the Spanish govt. to claim they are following democratic processes to enforce a very undemocratic rule. They seem to be playing with semantics to enforce their will.
Disclaimer: Total outsider view, I'm neither from Spain or Catalan nor have I ever visited. My opinions are based solely on news reports.
That remains to be seen. There are still less than 50% proponents of independence, according to what I read. The recent Spanish actions may have increased that number though.
(It's my opinion that it's _not_ justified, though: there's a fair chance of getting through the necessary changes to allow a referendum and other self-government demands by following legal procedures, given the current Spain-wide political climate. I believe this is mainly a politically dishonest and populist move by the Catalan government. But that's besides the point.)
MPs all over Europe (Denmark, Switzerland, Finland to name a few) have asked the Spanish government to stop prosecuting and negotiate a referendum.
Not only it is the judge's job: it's not even legal for a judge to knowingly allow an illegal action.
We don't even have to imagine. It happened recently: Scotland. Or if you allow me to jump the pond: Québec.
Also, indyref not ruled illegal yet so it might not be that clear cut.
Of course, the American Revolution was also illegal by the laws of the British.
It's also oppressive in the sense of trying to rule people without their consent.
If you try to let people choose, but the other side says no, what's there left to do?